1. Field of the Invention
This invention relates generally to storage networks and, more specifically, to selective file migration in a storage network.
2. Description of Related Art
In a computer network, NAS (Network Attached Storage) file servers connected directly to the network provide an inexpensive and easily configurable solution for a storage network. These NAS file servers are self-sufficient because they contain file systems that allow interoperability with clients running any operating system and communication using open protocols. For example, a Unix-based client can use the NFS (Network File System) protocol by Sun Microsystems, Inc. of Santa Clara, Calif. and a Windows-based client can use CIFS (Common Internet File System) by Microsoft Corp. of Redmond, Wash. to access files on a NAS file server. However, the operating system does not affect communication between the client and file server. Thus, NAS file servers provide true universal file access.
By contrast, more expensive and powerful SAN (Storage Area Network) file servers use resources connected by Fibre Channel on a back-end, or a dedicated network. A SAN file system is part of the operating system or an application running on the client. But heterogeneous client operating systems may require additional copies of each file to be stored on the storage network to ensure compatibility on the SAN file server. Additionally, communication between file servers on a SAN use proprietary protocols and thus are typically provided by a common vendor. As a result, NAS file servers are preferred when price and ease of use are major considerations. However, the benefits of NAS storage networks over SAN storage networks also have drawbacks.
One drawback with NAS file servers is that there is no centralized control. Accordingly, each client must maintain communication channels between each of the NFS file servers separately. When NAS file servers are either added or removed from the storage network, each client must mount or unmount directories for the associated storage resources as appropriate. This is particularly inefficient when there are changes in hardware, but not in the particular files available on the network, such as when a failing NAS file server is swapped out for an identically configured back-up NAS file server.
A related drawback is that a client must be reconfigured each time a file is relocated within the storage network, such as during file migration or file replication. The client generates a NAS file handle that identifies a physical location of the directory or file object on the file server. To access the object, the client sends an object access request directly to the NAS file server. When the file is relocated to a different NAS file server, subsequent requests for access to the file require a new look-up to locate the file and generate a new NAS file handle.
An additional drawback is that NAS file servers can become consumed with handling I/O (Input/Output) requests associated with file manipulations and accesses. As a result, additional processing tasks such as queries can unduly burden the NAS file servers. The file server typically walks a tree-structured directory tree in search of information requested by the query, and if there is more than one file system, each file system is individually walked. Consequentially, the file server may either become less responsive to I/O requests or have high latency in responding to the query. In some contexts, high latency will make the results stale.
Furthermore, NAS file servers can become unorganized and inefficient by, for example, storing critical data with other non-critical data. For example, large multimedia collections of MP3s used for leisure by employees can increase latency time in receiving information more germane to the productivity of an enterprise such as financial records. In another example, rarely accessed files may be stored on a premium, high bandwidth file server while often accessed files may be stored on a commodity, lower bandwidth server.
Therefore, what is needed is a network device to provide selectively migrate objects between file servers on a storage network. Furthermore, there is a need for identifying files to be migrated without burdening the file servers in, for example, servicing I/O requests.